This invention relates to a method and apparatus related to pumps and filter assemblies. A particular application of the invention is to aquatic situations such as ponds and aquariums and the like, but the method and apparatus is applicable outside this field.
There is disclosed in our granted prior patent GB2 293 333B a pump and filter assembly having great practical utility in which provision is made for automatic backflushing of the filter by a corresponding flow of the liquid medium being filtered.
We have discovered that the assembly disclosed in our prior patent is susceptible of improvement in respect of the backflushing function as explained below.
We have determined that there would be benefit in providing an improved system for regulating the fluid pressure in the supplies from the pump assembly to, respectively, the pump output (typically a fountain or something of that sort in an aquatic situation), and the supply of fluid to the filter backflushing assembly itself.
Typically, what happens in normal usage with the prior system disclosed in GB 27293 333 is that when the back pressure on the main output line is increased, the flow to the backflushing system increases. This is because the backflushing supply is taken from a T-connection on the output from the pump, the increase in the resistance to the flow from the pump in the main output line therefore causes an enhanced flow to the backflushing assembly. In simple terms the pump output takes the line of lesser resistance, which with increased resistance in the main output line will be, to the backflush assembly. With increased resistance in the main output line however the overall outlet flow from and through the pump will decrease. This occurs particularly in the case of a centrifugal pump, where the pump output increases as the resistance in the pump output line decreases. Consequently there is less need for the backflushing since less overall flow is entrained into the assembly and so less blockage occurs. The increase in backflushing flow in this situation is therefore not required. In fact this increase in backflushing flow in this situation is undesirable since it diverts flow and pump effort from the main output line.
In the opposite situation when the resistance in the main output line decreases the reverse occurs. Namely the flow in the main output line increases and the backflushing flow will be reduced. Overall though the flow through the pump will increase. However with the overall flow increasing there is more likelihood of the filter being blocked and so what would ideally be required is an increase in the backflushing flow in such a situation.
It can therefore be seen that with the arrangement disclosed in GB 2,293,333 the changes in backflushing flow in response to changes in the main output line resistance and overall flow are the opposite of what would desirably be required.
Having discovered this latter factor, we have invented a solution to the problem whereby the tendency for the backflushing supply to increase when the main pump output resistance increases and the main output flow decreases, is at least partially offset and/or which provides improvements generally to pump and filter assemblies.
According to a first aspect of the present invention there is provided a combined pump and filter assembly as described in the appended claims 1 to 12.
According to a second aspect of the present invention there is provided a method of operating a combined pump and filter assembly as described in appended claims 13 to 16.
Accordingly, in its broadest aspect, the present invention seeks to provide a means whereby the tendency for the backflushing supply to increase when the main output is subjected to increased flow resistance, is offset at least in part.
In one embodiment, this offsetting effect is achieved by the provision of dual pumping means. In the embodiment, the increased flow resistance in the output from one of the pumping means (the main pumping means) reduces its output flow, but does not reduce to the same extent the output flow in the other pumping means. Where the dual pump means are entirely separate, there is effectively little or no output effect on the second pumping means, except if they have a common drive and the increased load on the main pump slows down the second pump.